As one type of a braking-driving-force control apparatus for a vehicle such as an automobile, there has conventionally known a driving force control apparatus which controls distribution of driving force to left and right wheels so as to impart a predetermined yaw moment to a vehicle, as described in, for example, Japanese Patent Application Laid-Open (kokai) No. H9-309357. Further, there has already been known a braking force control apparatus which controls the braking-driving force and yaw moment of a vehicle, through control of braking forces of individual wheels, so as to secure the traveling stability of the vehicle. When such a braking-driving-force control apparatus is employed, the traveling stability of the vehicle can be improved.
In general, the braking-driving forces and yaw moment of a vehicle can be controlled through control of braking-driving forces of individual wheels. However, since there is a limit on the braking and driving force that each wheel can generate, in some cases, the braking-driving force or yaw moment required for the vehicle exceeds a level which can be attained through control of the braking-driving forces of the individual wheels. In conventional braking-driving-force control apparatuses as described above, such cases are not taken into consideration, and an improvement on that point has been demanded.
For example, there exist a case where a road surface in contact with front wheels or rear wheels has a low friction coefficient and a braking-driving force which can be generated by the wheels is smaller than a braking-driving force that can be generated by a braking-driving-force generation means, and a case where the maximum braking-driving forces that can be generated by the braking-driving-force generation means of the front wheels and the rear wheels differ from each other. In such cases particular, the magnitudes of the braking-driving force and yaw moment which can be attained by means of the braking-driving forces of the front wheels differ from those which can be attained by means of the braking-driving forces of the rear wheels. Therefore, in order to enable the braking-driving force and yaw moment required for the vehicle to be attained to a possible extent even in such a state, the braking-driving forces of the individual wheels must be controlled properly.